Carboranes and derivatives thereof have been and are being used as burning rate catalysts for solid propellant compositions. Normal-hexylcarborane and carboranylmethyl, -ethyl, or -propyl sulfide are typical carborane derivatives which are catalyst-plasticizer compounds that have been used for high burning rate propellants.
Inorganic and organic iron and iron-containing compounds have also been employed in propellants as burning rate catalysts. Ferrocene and ferrocene derivatives are typical of the organoiron compounds which have been used as burning rate catalysts.
Various theories and proposed mechanisms for the acceleration of propellant burning rates have evolved from experimentation in the field of catalysis. Apparently, the rate-controlling step for uncatalyzed propellant burning rates is determined mainly by the rate at which ammonium perchlorate undergoes decomposition. The burning rates of propellants increase as the particle size of the ammonium perchlorate is reduced. Smaller particle sizes facilitate the decomposition rate of ammonium perchlorate.
Very fine particle-sized (e.g. of only a few microns average mean-weight-diameter particle size) ammonium perchlorate in conjunction with catalysts (which have been incorporated in the propellant composition as liquid plasticizers) have been responsible for achieving ultrahigh burning rates for propellant compositions. The use of the liquid-type burning rate catalysts, however, has lead to other problems which include catalyst-plasticizer migration into the liner-insulation system.
The migration of liquid catalysts into the liner-insulation material can be eliminated by the use of a mixed intramolecular perchlorate salt: carboranyldiferrocenylmethyl perchlorate. The salt was disclosed and claimed in my U.S. Patent Application Ser. No. 120,682, filed Mar. 3, 1971. The activity of the compound is attributed to two different mechanisms for burning rate catalysis plus the oxidizer function which is derived from the perchlorate. Although the catalyst with both carboranyl and ferrocenyl funnctional groups has provided beneficial results, the carboranyl functional group alone has proven to be an excellent catalyst. The liquid carborane system does have, however, the undesirable feature of catalyst migration. Therefore, a solid carborane system would be highly desired since there would be no catalyst migration problem with a solid catalyst.
Desirable would be a propellant composition that employs a combination catalyst-oxidizer ingredient which can be used as a partial replacement for ammonium perchlorate without reducing the perchlorate ion content in the propellant composition. Advantageous would be the propellant composition employing a catalyst-oxidizer ingredient that is a solid ingredient and that has excellent compatibility with the other propellant ingredients. A catalyst-oxidizer ingredient which can be used as a replacement for the carborane catalyst-plasticizer in a propellant composition would be advantageous.
Therefore, an object of this invention is to provide a propellant composition which has improved burning rates and improved mechanical properties when the liquid catalyst-plasticizer is replaced with a catalyst-oxidizer ingredient.
Another object of this invention is to provide a propellant composition which employs a catalyst-oxidizer propellant ingredient that is stable with other propellant ingredients and that does not migrate into the liner-insulation system.
Still a further object of this invention is to provide a propellant composition which uses a lesser total amount of catalyst and ammonium perchlorate to thereby permit the use of a larger quantity of binder, and/or fuel, and/or oxidizer in the formulation to yield a propellant of high solids (metallic fuel, inorganic oxidizer) loading without adversely affecting the mechanical properties which is the situation which normally arises when the solids loading of a propellant is increased.